1. Field of the Invention
The present invention relates to a process for the generation of hydrogen and an apparatus having a catalytic combustor, reforming reactor and water gas shift reactor integrated in a single vessel assembly.
2. Description of the Related Art
Hydrogen is being considered as an alternative fuel for transportation and power generation. However, hydrogen has a low volumetric density making the storage and transport of hydrogen both difficult and costly. Thus, there is a need in the industry for efficient, small scale, onsite hydrogen generation.
Hydrogen may be generated in a number of ways. The technology of choice for large, refinery scale hydrogen production is steam reforming of methane (natural gas) followed by a water gas shift reaction.
In steam reformation, methane and hydrogen are reacted to form a reformate that includes carbon monoxide and hydrogen. Then, in a subsequent water gas shift reaction, carbon monoxide and water can be reacted to form carbon dioxide and hydrogen.
This is a mature technology and is one of the more cost effective methods for producing hydrogen from natural gas for smaller-scale distributed hydrogen generation. However, when used to produce a transportation fuel, distributed hydrogen generation is not cost competitive with gasoline on a dollar per gallon basis. In order for distributed hydrogen generation via steam methane reforming to be practical and cost competitive, the hydrogen production efficiency must be improved.
The main contributor to the low efficiency of smaller-scale steam methane reforming is heat loss. Heat loss is greatly exacerbated when the process is scaled down from large refinery plant capacity hydrogen production (>100,000 kg/day) to production levels on the order of several hundreds of kg/day or less. The increased heat losses at small scale contribute directly to low production efficiency, higher operating costs, and ultimately a higher cost of hydrogen.
The production efficiency problem has been addressed to a certain extent through re-design of heat exchangers, modified catalyst formulations and improved heat management. For example, it is known in the art to embed cooling coils and other heat exchangers within reactor vessels (catalytic combustor, reforming reactor and water gas shift) for the purpose of directing heat flows out of the reactor to an external heat exchanger, reactor or temperature control system. This approach typically requires extensive piping, a separate heat exchange fluid, and active flow controls. It is also known to recover otherwise un-utilized heat by combusting or oxidizing a waste gas from a purification step or fuel cell in a catalytic combustor. However, such features also typically employ separate reactor vessels, extensive piping and controls. Moreover, the heat recovery and efficiencies of such systems are generally not maximized because of heat loss and added parasitic losses due to complex active control systems.
Additionally, the initial capital equipment cost to build a small scale steam methane reforming facility contributes to the process not being competitive. Further, these designs have typically not been able to be manufactured at low cost because they require elaborate balance of plant components for active control and monitoring of process parameters.
Thus, the improvements have not advanced the technology far enough to make it commercially feasible.